Copper-base alloys having resistance to dezincification

ABSTRACT

Copper-base alloys are provided that maintain high hot forgeability and cuttability and low-cost feature and which still are improved in resistance to dezincification. The alloys comprise 57-69% of Cu, 0.3-3% of Sn and 0.02-1.5% of Si, all percentages based on weight, with a Si/Sn value in the range of 0.051, and the balance being Zn and incidental impurities.

[0001] This is a continuation-in-part application of U.S. Ser. No.09/891,650 filed Jun. 26, 2001.

BACKGROUND OF THE INVENTION

[0002] This invention relates to copper-base alloys having highresistance to dezincification corrosion which would otherwise occurduring use in corrosive aqueous solutions. The alloys also have good hotworking and cutting properties.

[0003] Cu—Zn alloys, commonly called brasses, have good workingproperties, both cold and hot, so they have found extensive use from oldtimes. Among the best known are forging brass bars (JIS C 3771),free-cutting brass bars (JIS C 3604) and high-strength brass bars (JIS C6782). These copper-base alloys share the common feature of including acontinuous β phase for better workability.

[0004] Zinc in the β phase has high ionization tendency, so in naturalenvironment, particularly in the presence of a corrosive aqueoussolution, it is selectively leached from the above-mentioned alloys.This is why those alloys are very poor in resistance to dezincification.

[0005] Various proposals have recently been made with a view toimproving the resistance to dezincification of brasses that aretypically used in parts that are brought into contact with water.According to Unexamined Japanese Patent Application (JPA) No.183275/1998, Sn is added to Cu—Zn alloys and, after hot extruding,various heat treatments are performed to control the proportion of the γphase and the Sn level in the γ phase, thereby improving resistance todezincification.

[0006] According to Unexamined Published Japanese Patent Application(JPA) No. 108184/1994, Sn is added to Cu—Zn alloys and, after hotextruding, the alloys are subjected to a heat treatment so that they aresolely composed of the a phase, thereby enhancing their resistance todezincification.

[0007] The new alloys described above are characterized by having Snadded in larger amounts than the conventional brasses. However, the highinclusion of Sn in brasses has its own problems.

[0008] First, with the increase in the Sn level, the localsolidification time of brasses increases and there occurs inversesegregation of Sn during casting, producing ingots with surface defects.At the same time, the adaptability to extrusion and other hot workingprocesses is impaired, causing a significant drop in the yield of shapedproducts.

[0009] Secondly, in order to elicit the ability of Sn to improveresistance to dezincification, hot extruding must be followed by a heattreatment for generating a certain area of γ phase at grain boundariesof the α phase and causing Sn to diffuse uniformly in the γ phase.However, this adds to the overall production cost.

[0010] What is specifically taught in JPA No. 183275/1998 is as follows:a heat treatment is applied at between 500° C. (inclusive) and 550° C.(inclusive) for at least 30 seconds, then cooling to 350° C. is done ata rate no faster than 0.4° C./sec; alternatively, a heat treatment isapplied at between 400° C. (inclusive) and 500° C. (inclusive) for atleast 30 seconds, then cooling is done; or a heat treatment is appliedat between 500° C. (inclusive) and 550° C. (inclusive) for at least 30seconds, then cooling to 350° C. is done at a rate between 0.4° C./sec(inclusive) and 4° C./sec (inclusive). The teaching of JPA No.108184/1994 comprises hot extruding or drawing the alloy, followed by aheat treatment at 500-600° C. for a period of 30 minutes to 3 hours.

[0011] These heat treatments involve various problems. For one thing, inorder to ensure the appropriate conditions, costly equipment must beused. Secondly, depending on product size, the difference in heatpattern between the interior and exterior of the product can causevariations in microstructure, which makes the process lesscost-effective due to lower yield. Thirdly, products of complex shapeoccasionally suffer from the problems of dimensional changes, residualstress and so forth.

[0012] A recent proposal worth particular mention is free-cutting copperalloys having Si added to Cu—Zn alloys (JPA Nos. 119774/2000 and119775/2000). These alloys contain at least 1.8 wt % of Si with a largeportion of Cu/Si γ phase at grain boundaries of the a phase. Underenvironment of actual use, the Cu/Si γ phase has better resistance todezincification than the β phase but is not as resistant as a Cu/Sn γphase. If the Si content is 1.8% or more, the thermal conductivity ofthe material drops considerably and the blade of a cutting tool becomesunduly hot during cutting to cause many problems such as a shorter lifeof the cutting tool, lower precision in cutting and limit on the cuttingspeed.

[0013] JPA 60-149740 proposes alloys having improved wear-resistanceprepared by adding to Cu—Zn alloys elements such as Al, Fe, Sn, Si andZr. These alloys are endowed with high strength and improvedwear-resistance by precipitating therein intermetallic compounds of Sn,Si, Zr and Fe. However, because these alloys show a small elongation,there is a problem in that they show poor cold workability. Moreover,since they contain a large number of elements, it is complicated tocontrol proportions of component elements in the course of casting. Thisis one of the important factors that adds to the cost of production.

SUMMARY OF THE INVENTION

[0014] The present invention has been accomplished under thesecircumstances and has as an object providing copper-base alloys thathave outstanding resistance to dezincification, hot forgeability,cuttability and elongation and which still can be fabricated atreasonably low cost.

[0015] The present inventors conducted intensive studies in order toensure that the addition of Sn would prove effective in preventingdezincification of copper-base alloys to the fullest extent and foundthe following: when Si as well as Sn were added and the weightpercentage ratio of Si to Sn was adjusted to lie in an appropriaterange, secondary dendrite arms grew sufficiently thinner and longerduring solidification to suppress segregation of Sn; upon hot working,the γ phase was dispersed uniformly between regions of a phase. Thisphenomenon made a great contribution to improvements in resistance todezincification and hot working properties.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The stated object can be attained by any one of the followingcopper-base alloys having improved resistance to dezincification.

[0017] (1) A dezincification resistant copper-base alloy consistingessentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si, and 0.5-3%of at least one of Pb and Bi, all percentages based on weight, with aSi/Sn wt % ratio value in the range of 0.05-1 and the balance being Znand incidental impurities.

[0018] (2) A dezincification resistant copper-base alloy consistingessentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% ofat least one of Pb and Bi, all percentages based on weight, with a Si/Snwt % ratio value in the range of 0.05-1, further containing in a totalamount of 0.02-0.2% at least one element selected from the groupconsisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, allpercentages based on weight, and the balance being Zn and incidentalimpurities.

[0019] (3) A dezincification resistant copper-base alloy consistingessentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% ofat least one of Pb and Bi, all percentages based on weight, with a Si/Snwt % ratio value in the range of 0.05-1, further containing in a totalamount of 0.01-2% of at least one element selected from the groupconsisting of 0.01-0.3% of Fe, 0.01-0.5% of Ni, 0.01-0.5% of Cr,0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag,0.01-0.3% of Ti, 0.01-0.5 of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te,0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and0.01-0.5% of Ca, all percentages based on weight, and the balance beingZn and incidental impurities.

[0020] (4) A dezincification resistant copper-base alloy consistingessentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% ofat least one of Pb and Bi, all percentages based on weight, with a Si/Snwt % ratio value in the range of 0.05-1, further containing in a totalamount of 0.02-0.2% at least one element selected from the groupconsisting of 0.02-0.2% of P, 0.02-0.2% of Sb and 0.02-0.2% of As, stillfurther containing in a total amount of 0.01-3% of at least one elementselected from the group consisting of 0.01-0.3% of Fe, 0.01-0.5% of Ni,0.01-0.5% of Cr, 0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce,0.01-0.5% of Ag, 0.01-0.3% of Ti, 0.01-0.5% of Mg, 0.01-0.5% of Co,0.01-0.5% of Te, 0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La,0.01-0.5% of Cd and 0.01-0.5% of Ca, all percentages based on weight,and the balance being Zn and incidental impurities.

[0021] On the following pages, the criticality of the compositionalranges for the ingredients in the copper-base alloy of the invention isdescribed in detail.

[0022] Cu:

[0023] An increase in the Cu content adds to the α phase and improvescorrosion resistance but if its content exceeds 69%, there occurs amarked drop in hot forgeability. Since Cu is more expensive than Zn, theCu content is desirably minimized from an economical viewpoint. If theCu content is smaller than 57%, the proportion of the β phase increasesto improve forgeability at elevated temperature; on the other hand,resistance to dezincification decreases and so do the strength andelongation of the material. Considering these merits and demerits, thecompositional range of Cu is specified to lie between 57 and 69%,preferably between 59 and 63%, on a weight basis.

[0024] Sn:

[0025] Adding at least 0.3% of Sn is effective in improving resistanceto dezincification. What is more, the improvement in resistance todezincification is marked if the addition of Sn is increased. However,adding Sn in excess of 3% not only induces deep defects in the surfaceof ingots being cast but also fails to bring out a correspondingimprovement in the resistance to dezincification. In addition, Sn ismore expensive than Zn and Cu, so it is a factor in increasing theproduction cost. For these reasons, the content of Sn in the copper-basealloy of the invention is specified to lie between 0.3 and 3%,preferably between 0.5 and 2%.

[0026] Si:

[0027] Silicon is added for the particular purpose of improvingcastability and eliciting the ability of Sn to improve resistance todezincification. Adding a suitable amount of Si is effective inimproving the fluidity of a melt during casting and suppressing thesegregation of Sn. As a result, in the absence of any heat treatmentafter hot extruding and forging, the ability of Sn to improve resistanceto dezincification is elicited to the fullest extent, thereby providingconsistent and outstanding dezincification resistance and mechanicalcharacteristics.

[0028] If the Si content exceeds 1.5%, an increased amount of Si/Cu γ, κor β phase appears at grain boundaries of the a phase to deteriorate theresistance to dezincification. In addition, the increased amount of Sioxide is detrimental to castability and hot workability. If the Sicontent further increases to 1.8% or more, the thermal conductivity ofthe material drops considerably and the blade of a cutting tool becomesunduly hot during cutting to cause many problems such as a shorter lifeof the cutting tool, lower precision in cutting and limit on the cuttingspeed.

[0029] If the Si content is less than 0.02%, there is obtained no effectof improving castability or suppressing the segregation of Sn. For thesereasons, the compositional range of Si is specified to lie between 0.02and 1.5%, preferably between 0.06 and 0.6%.

[0030] Si/Sn:

[0031] The Si/Sn value is specified in the present invention since inorder to maximize the ability of Sn to improve resistance todezincification, Si must be added in an optimum amount that depends onthe amount of Sn addition.

[0032] Generally, the 60/40 brass has a two-phase structure consistingof α-phase+β-phase, wherein β-phase has poorer resistance todezincification than α-phase. Tin (Sn) dissolves more in β-phase than inα-phase and enhances resistance to dezincification. If tin is added inan amount of 0.5% or more, however, precipitation of γ-phase isobserved. The γ-phase is hard and brittle and so it makes the materialmore brittle. In addition, since the γ-phase dissolves a larger amountof Sn, it impairs the ability of α- and β-phases as a matrix to resistdezincification. On the other hand, since the zinc equivalent of Si isas high as 10, its addition is effective to decrease the precipitationof γ-phase and increase the proportion of β-phase. For this reason theaddition of Si is effective in enhancing hot workability and inembrittling the material at ordinary temperatures. By controlling theSi/Sn ratio at an appropriate level, effect of Sn to resistdezincification can be obtained, retaining the (α+β)-phase structure asit is.

[0033] Moreover, if Si is added under the condition that the Si/Sn ratiois controlled at an appropriate level, secondary dendrite arms grow in asufficiently finer and longer form during solidification to suppress thesegregation of Sn and, after hot working, the γ phase is disperseduniformly between regions of a phase to improve resistance todezincification while assuring hot deformability. If the Si/Sn value isgreater than 1, the volume of β-phase increases, the Sn content in theβ-phase correlatively decreases. This makes it difficult to obtainsufficient effect of resisting dezincification. Since Si has a smallmolecular weight and strongly affects the formation of solid-solutions,an unduly large amount of addition of Si may be linked to roomtemperature enbrittlement of the material. If the Si/Sn ratio is smallerthan 0.05, the intended effect of suppressing the segregation of Sn isnot fully attained and the (α+β+γ) three-phase structure is easy todevelop, which makes it difficult to obtain the effect of resistingdezincification. Therefore, the Si/Sn ratio is preferably in the rangeof 0.05-1, more preferably in the range of 0.1-0.5.

[0034] P, Sb, As:

[0035] These elements are effective in suppressing dezincificationwithout impairing cuttability and forgeability. If their addition isless than 0.02%, the intended effect of suppressing dezincification isnot obtained. If their addition exceeds 0.2%, boundary segregationoccurs to reduce ductility while increasing stress corrosion crackingsensitivity. Hence, the contents of P, Sb and As are each specified tolie between 0.02 and 0.2%.

[0036] Pb, Bi:

[0037] At least one of lead and bismuth is added to improve thecuttability of the material. If its addition is less than 0.5%, thedesired cuttability is not attained. If the Pb and/or Bi additionexceeds 3%, hot working such as extruding or forging is difficult toperform. If Pb and/or Bi is to be added, its compositional range, eachor in total, is between 0.5 and 3%, preferably between 1.5 and 2.3%.

[0038] If desired, the copper-base alloy of the invention may furthercontain at least one element selected from the group consisting of0.01-0.3% of Fe, 0.01-0.5% of Ni, 0.01-0.5% of Cr, 0.01-0.5% of Be,0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag, 0.01-0.3% of Ti,0.01-0.5% of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te, 0.01-0.5% of Au,0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and 0.01-0.5% of Ca;these elements may be contained in a total amount of 0.01-3%. If addedin amounts within the specified ranges, these elements are effective inimproving mechanical characteristics and cuttability without damagingresistance to dezincification and hot workability. Moreover, since thepresence of the above-listed elements is allowable, scraps can be usedeasily. This fact contributes to the reduction of the production cost.However, if the contents of the above-listed elements exceed the rangesspecified above, they form intermetallic compounds with Si and/or Sn,thereby hindering the effect of improving resistance to dezincification,and at the same time the elongation decreases due to the precipitationhardening.

[0039] If in a small amount the addition of Al or Mn neither impairs norenhances characteristic properties such as resistance todezincification, hot forgeability, cuttability and the like.

[0040] The meaning of the addition of Al or Mn is described below indetail.

[0041] Al:

[0042] Aluminum is not only effective in forming a solid-solution in theCu—Zn alloy to enhance its strength but also upon being rubbed diffusesinto the surface of the alloy to form there Al₂O₃ and contribute toimproving its wear-resistance. However, increase in strength due to theformation of a solid-solution of Al is too big to keep good workabilityof the material. For example, JP-60149740 shows in Example 1 that thealloys disclosed therein have tensile strength of approximately 700 Mpaand elongation of 10-15%. This means that the alloys of JP-60149740 areinferior in their workability at room temperature to the alloys of thepresent invention that have elongation of not less than 20%.

[0043] Mn:

[0044] Manganese (Mn) forms an intermetallic compound with Si thatprecipitates uniformly in the form of fine dispersed particles toincrease strength and wear-resistance of the material. However, silicon(Si) dissolves in the Cu—Zn matrix to impair the effect of enhancingresistance to dezinfication.

[0045] Both JPA 60-149740 and JPA 62-274036 relate to alloy materialswhose strength and wear-resistance have been enhanced by precipitatingtherein the elements added thereto in the form of their intermetalliccompounds. Accordingly, elements such as Fe and Zr that are easy to formintermetallic compounds are selectively used as requisite elements. Inparticular, elements such as Zr and Mn are easy to form intermetalliccompounds with Sn and Si. Thus, the presence of these elements hindersSn and Si to dissolve in the matrix to enhance resistance todezincification. The alloys disclosed in JPA 11-1736 are out of thescope of the present invention because they contain neither Sn nor Siand the invention disclosed therein does not relate to the improvementof “resistance to corrosion” but relates to the improvement of“resistance to high temperature corrosion” which is quite different to“resistance to dezincification”. The alloys shown in the workingexamples of JPA 11-1736 cannot satisfy the resistance to dezincificationand hot forgeability desired and attained by the present inventors.

[0046] In summary, all the alloys disclosed in the JPA 60-149740, JPA62-274036 and JPA 11-1736 have been developed bearing wear-resistance inmind. For this reason the elements added are precipitated in theresulting alloys in the form of intermetallic compounds so as to obtainhigh strength and high wear-resistance. Moreover, Al is added to obtainimproved resistance to corrosion by marine water. The addition of Al iseffective to improve resistance to corrosion by marine water and acid ofthe entire matrix of the alloy. But it is not very much effective toenhance the resistance to dezincification of the alloy. In contrast, inthe present invention appropriate amounts of Sn and Si are added todissolve in the matrix for the purpose of enhancing resistance todezincification. The alloys of the present invention include the usesfor which good cuttability at room temperature and good caulking abilityare required. Therefore, the alloys are desired to possess superiorparting properties as well as elongation of not less than 20%. Thus, itis evident that no alloys disclosed in the above references can satisfyall of the above-recited requirements in view of the known capabilitiesof the elements added to the alloys.

[0047] The copper-base alloy of the invention with its compositionadjusted to the ranges set forth above has outstanding resistance todezincification, hot forgeability and cuttability and still can befabricated at reasonably low cost.

[0048] The mode for carrying out the present invention is describedbelow with reference to examples.

EXAMPLES

[0049] Samples of the dezincification resistant copper-base alloy of theinvention were prepared as described below. Comparative samples werealso prepared. The chemical ingredients listed in Table 1 were melted inan induction furnace and cast semicontinuously into billets (80 mm^(φ))at temperatures of the liquidus plus about 100° C. The castability ofeach composition was evaluated by checking the depth of surface defectssuch as inclusions in the cast billets. The results are shown in Table 1as evaluated by the following criteria: ⊚ (depth of surface defect<1mm); ∘ (1-3 mm); X (>3 mm). Sample Chemical ingredients (wt %) No. Cu ZnSn Si Si/Sn Pb Bi P Fe Al Zr Ni  1 Invention 61.3 bal. 1.50 0.71 0.4731.7 — — — — — —  2 59.5 bal. 1.38 0.65 0.471 1.8 — — — — — —  3 60.2bal. 1.40 0.63 0.450 1.9 — 0.07 — — — —  4 58.5 bal. 2.50 0.24 0.096 2.0— — — — — —  5 60.7 bal. 1.08 0.20 0.185 2.0 — 0.04 0.11 0.02 — —  661.2 bal. 0.87 0.21 0.241 1.9 — 0.05 0.13 — 0.08 0.17  7 61.8 bal. 1.000.12 0.120 1.7 — 0.05 0.10 0.11 — 0.30  8 61.2 bal. 1.50 0.18 0.120 1.6— 0.07 0.17 — — —  9 59.0 bal. 1.50 0.36 0.240 1.4 — 0.08 0.23 — — 1 1062.0 bal. 1.30 0.66 0.508 1.4 0.05 0.05 — 11 60.2 bal. 1.10 0.45 0.4091.8 0.03 0.23 — — 0.60 12 Comparison 62.0 bal. 1.50 — — 1.9 — — — — — —13 60.6 bal. 0.46 1.00 2.174 2.0 — 0.05 — — — — 14 59.0 bal. 0.20 0.010.050 — — 0.04 — — — — 15 58.0 bal. — 2.5 — 1.9 — — — — — — 16 61.0 bal.— 3 — — — — — — — — 17 59.0 bal. 1.5 1.9 1.267 — — — — — — —

[0050] The 80-mm^(φ) billets were held at 800° C. for 30 minutes andlater hot extruded into bars having a diameter of 30 mm.

[0051] The as-extruded bars were evaluated for resistance todezincification, resistance to hot deformation, hardness, tensilestrength and elongation. The dezincification test was conducted by twomethods under different conditions, one specified in JBMA T303-1988 andthe other in ISO 6509-1981. Test samples as cut from the extruded barswere set so that the direction of corrosion coincided with the extrudingdirection. In order to investigate the extent of the change inresistance to dezincification that was caused by heat treatment,evaluation was also made for the resistance to dezincification ofsamples that were subjected to a heat treatment at 400° C. for 3 hours.

[0052] To measure the resistance to hot deformation, cylindrical samples15 mm in both diameter and height were cut on a lathe from the extrudedbars and subjected to a drop-hammer test. The test temperature and thedistortion rate were 750° C. and 180 s⁻¹, respectively.

[0053] The cutting test was performed by cutting on a lathe and chipfragmentation was evaluated by the following criteria: ∘ (all chips werecompletely fragmented); X (chips were not fragmented). For stickingproperty, 10 cutting tests were conducted with a continuous feed of 100mm and the results were evaluated by the following criteria: X (copperstuck to the tip of the blade); ∘ (no copper stuck). The cuttingconditions were as follows: rotating speed, 950 rpm; depth of cut, 0.5mm; feed speed, 0.06 mm/rev.; feed, 100 mm; cutting oil, none; cuttingtool material, superhard steel. The hardness of the copper-base alloywas Vickers hardness and measured according to JIS Z 2244 under atesting force of 49 N on a section perpendicular to the extrudingdirection. The tensile test was conducted in accordance with JIS Z 2241on No. 4 specimens which were stretched in a direction parallel to theextruding direction. The results of the tests are shown in Table 2.TABLE 2 Resistance Maximum depth of to hot Chip Hard- Tensile Elonga-dezincification Sample Cast- deformation fragment- ness strength tionafter heat No. ability MPa ation Hv MPa % as-extruded treatment  1Invention ⊚ 78 ∘ 130 451 27 59 59  2 ⊚ 67 ∘ 132 445 28 65 64  3 ⊚ 67 ∘129 433 34 60 60  4 ∘ 72 ∘ 141 452 25 41 39  5 ⊚ 75 ∘ 107 407 45 57 55 6 ⊚ 76 ∘ 105 399 46 59 58  7 ⊚ 74 ∘ 110 445 45 57 56  8 ⊚ 73 ∘ 118 41844 53 51  9 ⊚ 68 ∘ 133 467 44 52 52 10 ⊚ 69 ∘ 128 410 25 58 54 11 ⊚ 69 ∘120 422 27 60 53 12 Comparison X 79 ∘ 119 412 36 92 71 13 ⊚ 67 ∘ 132 42325 115 116 14 ⊚ 85 X 98 387 48 173 167 15 X 75 ∘ 140 440 21 134 135 16 X73 X 146 453 19 165 171 17 X 65 X 165 527 26 155 157

[0054] Sample Nos. 1-11 prepared in accordance with the alloycomposition of the invention showed outstanding castability, mechanicalcharacteristics and cuttability, as well as low resistance to hotdeformation comparable to that of hot forging alloy C 3771 (deformationresistance, 70 MPa). They all had high resistance to dezinciticationsince the maximum depth of dezincification was no more than 65 μm inJBMA T303-1988 and no more than 130 μm in ISO 6509-1981.

[0055] What was particularly interesting about the samples of theinvention was that the maximum depth of dezincification as measured byJBMA was little different between the as-extruded state and theheat-treated state. It was therefore clear that by adding suitableamounts of Si, the copper-base alloys were given consistent andoutstanding resistance to dezincification even when they were justsubjected to hot working without any subsequent special heat treatments.

[0056] Sample Nos. 12-17 were comparisons and had various defects.Sample No. 12 did not contain Si, so it was not only low in castabilityand resistance to dezincification but also characterized by considerabledifference in the maximum depth of dezincification between theas-extruded state and the heat-treated state. Sample No. 13 had a Si/Snvalue beyond the range specified by the invention, so an excessive βphase surrounded the α phase, deteriorating the resistance todezincification.

[0057] Sample No. 14 contained less Sn and Si than the lower limitsspecified by the invention, so the proportions of the γ and κ phaseswere insufficient to prevent marked drop in resistance todezincification; what is more, the resistance to hot deformation wasgreat and chips could not be fragmented. Sample Nos. 15 and 16 did notcontain Sn, so they were poor in resistance to dezincification; inaddition, they contained more Si than specified by the invention, socopper stuck to the tip of the cutting blade showing how poor thecuttability of the material was.

[0058] Sample No. 17 contained both Sn and Si but the Si/Sn valueexceeded the range specified by the invention; what is more, the Sicontent was greater than 1.8%. Hence, the sample was poor in resistanceto dezincification and castability and copper stuck to the tip of thecutting blade.

[0059] As described above, the present invention offers copper-basealloys that have outstanding resistance to dezincification, hotforgeability and cuttability and which still can be fabricated atreasonably low cost.

What is claimed is:
 1. A dezincification resistant copper-base alloyconsisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Siand 0.5-3% of at lest one of Pb and Bi, all percentages based on weight,with a Si/Sn value in the range of 0.05-1, and the balance being Zn andincidental impurities.
 2. A dezincification resistant copper-base alloyconsisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% of Siand 0.5-3% of at least one of Pb and Bi, with a Si/Sn value in the rangeof 0.05-1, further containing in a total amount of 0.02-0.2% at leastone element selected from the group consisting of 0.02-0.2% of P,0.02-0.2% of Sb and 0.02-0.2% of As, all percentages based on weight,and the balance being Zn and incidental impurities.
 3. A dezincificationresistant copper-base alloy consisting essentially of 57-69% of Cu,0.3-3% of Sn, 0.02-1.5% of Si and 0.5-3% of at least one of Pb and Bi,with a Si/Sn value in the range of 0.05-1, further containing in a totalamount of 0.01-2% of at least one element selected from the groupconsisting of 0.01-0.3% of Fe, 0.01-0.5% of Ni, 0.01-0.5% of Cr,0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag,0.01-0.3% of Ti, 0.01-0.5% of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te,0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and0.01-0.5% of Ca, all percentages based on weight, and the balance beingZn and incidental impurities.
 4. A dezincification resistant copper-basealloy consisting essentially of 57-69% of Cu, 0.3-3% of Sn, 0.02-1.5% ofSi and 0.5-3% of at least one of Pb and Bi, with a Si/Sn value in therange of 0.05-1, further containing in a total amount of 0.02-0.2% atleast one element selected from the group consisting of 0.02-0.2% of P,0.02-0.2% of Sb and 0.02-0.2% of As, still further containing in a totalamount of 0.01-3% of at least one element selected from the groupconsisting of 0.01-0.3% of Fe, 0.01-0.5 of Ni, 0.01-0.5% of Cr,0.01-0.5% of Be, 0.01-0.3% of Zr, 0.01-0.5% of Ce, 0.01-0.5% of Ag,0.01-0.3% of Ti, 0.01-0.5% of Mg, 0.01-0.5% of Co, 0.01-0.5% of Te,0.01-0.5% of Au, 0.01-0.5% of Y, 0.01-0.5% of La, 0.01-0.5% of Cd and0.01-0.5% of Ca, all percentages based on weight, and the balance beingZn and incidental impurities.